1. Field of the Invention
The present invention is generally directed to a method for the treatment of gas wells with a treatment fluid and the apparatus used in the inventive method. More particularly, the method is useful for the treating of flowing gas wells with an anticorrosion treatment fluid.
2. Background
Natural gas is produced from wells that are drilled into underground formations which contain geologically formed mixtures of methane, ethane, propane, and other gaseous hydrocarbons. In addition to the useful hydrocarbons, other gases may have formed with the natural gas that are corrosive to the metal production tubing string through which the gas is brought to the surface. Over time these naturally occurring corrosive gases cause the formation of scale and create corrosion problems on the inner surface of the production tubing string of the flowing gas well. If this condition is left untreated, the production tubing string will eventually fail causing a costly and unsafe uncontrolled release of the natural gas.
In order to prevent corrosion and scale build-up within the producing pipe string, the inside of the production tubing string is treated with conventional corrosion inhibitors. The success in treating the inner surface of the production tubing string depends upon the ability of to apply a protective film or layer of corrosion inhibitor along the entire length of the production tubing string. There are several methods for attempting to achieve this goal.
The most common method used to treat the production tubing string of flowing gas wells is the "batch and fall" method. The "batch and fall" method is carried out by stopping the flow of gas (i.e. stopping production) and introducing a given volume of treatment fluid into the wellhead end of the production tubing string. The treatment fluid is usually followed by a flushing fluid which helps force the treatment fluid down the production tubing string. The treatment fluid and the flush fluid are then allowed to "fall" though the length of the production tubing string thus coating its inside surface with treatment fluid. Typically the fall rate will be anywhere from 1000 feet per hour (305 meters per hour) to 3000 feet per hour (915 meters per hour). The fall rate depends upon many factors including the viscosity of the treatment fluid, the diameter of the production tubing string, the natural gas pressure of the well, and so forth. Because of these variables, the time required for the complete treatment of the production tubing string is unpredictable. If the well is returned to production too soon, the treatment fluid will not have coated the entire length of the production tubing string thus leaving the bottom of the production tubing string unprotected. However, if the well is left off production for too long, the treatment fluid and the flushing fluid may migrate into the gas producing formation. This latter case is undesirable because the fluids might cause damage to the formation and prevent or inhibit the flow of natural gas from the underground formation.
Several methods of treating the inner surface of a production tubing string have been previously described and for one reason or another have had only limited success or less than desirable results. Examples of such methods include squeeze treatment and tubing displacement. Both of these methods are less commonly utilized because they are more expensive than batch and fall methods and increase the chance of formation damage. Other unpopular methods include using nitrogen gas to flush the treatment fluid down the production tubing string, using aerosol type inhibitors, or using specially weighted inhibitors, inhibitor stick or brush applicator tools to make the application more uniform and predictable. The last noted of these methods, utilizes a brush applicator tool to push the treatment fluid through the production tubing string while at the same time the brush "paints" the treatment fluid onto the inside surface of the production tubing string. The rate at which the brush applicator applies the treatment fluid is approximately 125 feet per minute (38 meters per minute). The primary problem with this latter method is that although it is faster than the batch and fall treatment method, the time required for the complete application of the treatment fluid is longer than desired.
Therefore there exists a continuing need for improved methods of applying treatment fluid on the inside surface of the production tubing string of a gas well.